First Part:
European nations and Japan typically saught many colonies for resources. Let me explain. Let us say you live on a rock in the vast ocean, you have a large fleet and standing army but you don't have enough food to feed them, let alone the people. So what do you do? You attack a neighbor with a smaller army to grow food. If that is not enough then you attack some more, and then more, until you own the entire world or are crushed by a larger enemy. This was the same thing Japan did and was eventually crushed by the united states.